The invention relates to an implantable tube for injecting fluid into all or a part of a human or animal tissue. In the rest of the specification, the invention is described more particularly in relation to the injection of heat transfer fluid. However, the tube may also be used for injecting cold substances such as, for example, suspensions of magnetic nanoparticles or nanocapsules containing one or more active materials.
One of the methods for treating cancerous tumours consists in destroying all or part of the cancerous tissue by the targeted administration of heat or cold. This principle is known by the name “thermoablation” and is currently used in particular for treating liver metastases.
Many techniques based on the principle of heat-induced thermoablation are proposed today, such as laser, radio-frequency with needle, cryotherapy, which pertains to cold-induced thermoablation. However, these techniques have a number of drawbacks. In particular, the volume of the tumour treated remains limited (in practice 4 to 5 cm in diameter) and the operating time is relatively long, 20 to 30 minutes for radio-frequency and cryotherapy, even longer for laser treatment.
Document WO 00/29055 of the Applicant describes a heat-induced thermoablation technique whereby water or hydrogen peroxide is directly injected into the organism at a pressure of up to 3000 bar, at a temperature of 200 to 400° C. For this purpose, the hydrogen peroxide or water is heated in a metal coil incorporating an electrical resistor or a heat exchanger around which a platinum-iridium tube is wound. The alloy tube is connected to the diffusion means, which is in the form of a tube implanted directly into the tissue to be treated. This tube, referred to below as “microtube”, has an outside diameter of between 100 and 250 μm, and an inside diameter of between 50 and 150 μm. It is made from a material suitable for withstanding the pressure of 3000 bar such as, for example, a platinum/iridium alloy, so that, when it is connected to the heating coil, it is suitable for injecting water or hydrogen peroxide in vaporized form. The temperature of the vaporized liquid, in contact with the tissue to be treated, decreases and the water returns to the liquid state inside the tumour.
In document WO 03/070302, the Applicant proposes a thermoablation method improved in that it provides for injecting the heat transfer fluid no longer continuously, but in pulsed form. In practice, the volume of liquid injected is very small, for example, between 0.2 and 1 ml, thereby avoiding the diffusion of heat outside the tumour. Furthermore, these volumes are injected at regular intervals of between 0.5 and 1 second, thus reducing the quantity of heat outside the zone to be treated, and thereby facilitating the handling of the tube by the surgeon.
In the two methods proposed, the heating system remains unchanged and essentially consists of a metal coil incorporating an electrical resistor and around which a stainless tube in which the heat transfer fluid flows is wound.
This heating system has a number of drawbacks.
Firstly, its position upstream of the installation demands a heating power commensurate with the length of the extension between the actual microtube and the heating system. Moreover, this system does not permit a sequencing, without any dead time, of the pulsed injection of hot products and cold products, because the coil cooling time is too long.
Document U.S. Pat. No. 5,542,928 describes a catheter designed for thermoablation conveying a fluid flowing externally at the distal end of the said tube via perforations. In practice, the liquid flowing in the tube is heated using a helical resistor arranged on the distal portion of the catheter and connected to an electric power supply. The catheter described in this document is designed to be introduced into the cavities for which it is unnecessary to have a small-diameter tube, the diameter being in fact between 2 and 10 mm. The presence of the resistor further increases the final diameter of the device designed to be introduced into the organism. While this document describes the idea of heating only the distal part of the tube, the size of the system proposed remains incompatible with a direct implantation into the tissues.
Document U.S. Pat. No. 6,328,735 B1 describes a thermoablation technique combining hot liquid injection and radio-frequency. More precisely, as above, the installation described comprises a tube whereof the distal end is provided with a resistor for heating the liquid arriving at the end of the tube. Here also, the tube diameter is advantageously 2 mm and the tube is surrounded by a coil having a resistance of 50Ω.
Document U.S. Pat. No. 5,964,752 describes an apparatus of the same type as above, for treating cartilages. Here also, the distal end of the tube is provided with a resistor, positioned this time inside the tube.
In all the cases, the heating systems proposed require a coil-shaped resistor generating a high inductance, incompatible with the current pulses like those used by the Applicant, because this would cause an excessively high impedance.
Document WO 02/069821 describes a tube in which vapour flows, for implanting in the organism. The vapour is generated directly in the tube in which the fluid flows by radio-frequency. More precisely, the tube has two electrodes connected to a radio-frequency generator, the liquid conveying the current between the two electrodes. In the proposed system, there is no differential heating and the tube is heated along its whole length. Moreover, the choice of the liquid to be injected is limited to conducting liquids. Finally, the current flow in the liquid is liable to affect the properties thereof.
In other words, the problem that the invention proposes to solve is to develop an installation of the type described for example in document WO 03/070302, in which the heat transfer fluid is heated to the vaporization temperature, exclusively in the distal part of the implantable microtube, the tube diameter being 10 to 20 times smaller than that of a catheter conventionally used for thermoablation.
A second problem that the invention proposes to solve is to develop a system in which the inductance is zero, making it usable with current pulses.
A third problem that the invention proposes to solve is to provide a single installation for injecting heat transfer fluid or cold fluid conveying nanocapsules or nanoparticles, according to the type of treatment involved.
The Applicant has developed a microtube connected to an electric power supply having a structure whereby it has a resistance of between 0.2 and 2Ω in its distal part and a resistance lower than 0.01Ω in its remaining part.
In other words, the electric power is concentrated in the distal part of the tube, thereby serving to reach temperatures of about 400° C.
The new system developed consists of a microtube for direct implantation into the tissues, the microtube being devoid of an additional electrical resistance and having a distal end capable of reaching high heating temperatures, the tube itself acting as a heating resistor. This tube is connected via an extension conveying the cold liquid, to the liquid storage and injection unit.
In other words, the invention relates to an implantable tube, for heating by conduction in particular a heat transfer fluid for injection into all or part of a human or animal tissue, the tube being provided with a wall having distal, median and proximal parts and comprising means for direct or indirect connection of the distal part to a fluid reservoir, characterized in that it is provided with two means for connection to the terminals of an electric power supply, for incoming and outgoing current in the wall, and in that it has a resistance less than 0.01Ω in its median and proximal parts, and a resistance of between 0.2 and 2Ω in its distal part, the median and proximal parts being connected electrically in series to the distal part, the tube having no additional electrical resistance, and having a practically zero inductance.